In recent times, each one of the parts that comprise the assembly including the piston top, the piston skirt, the connecting rod and the wrist pin, to pivotally interconnect these parts, have been exhaustively studied, aiming a reduction in weight. This is to reduce the power losses caused by such moving metal parts and, therefore, take advantage of all the energy generated in the cylinder so as to decrease the fuel consumption and maintain the efficiency of the engine in desired levels.
Referring particularly to the wrist pin, it has traditionally been made of steel or iron. In the middle of the 1980's it was proposed to use plastics or polymers for its manufacture. A like proposal is found in the U.S. Pat. No. 4,430,906 of the Standard Oil Company.
However, in the most recent types of diesel engines having articulated pistons, the pressures and temperatures in the cylinder have increased by such an amount that it would be necessary to use sophisticated and very expensive polymers to meet such requirements of loads and temperatures.
Another approach for the problem is the reduction of material on walls of a conventional wrist pin made of steel or iron, as more recently disclosed in the U.S. Pat. No. 4,712,941, issued to Emmer and assigned to Chrysler Motors Corporation, as well as in U.S. Pat. No. 4,756,240, issued to Mielke and assigned to Kolbenschmidt. Alternatives of this type generally comply with most of the needs in terms of weight and resistance but, at the present time, they may be deemed improper, since the manufacturing methods are too complicated and therefore very costly.
More important than this is the fact that the known prior proposals do not provide a specific resistance which closely approximates the distribution of forces along the wrist pin length, which is different from that existing in like assemblies employing monolithic pistons, thereby resulting in pins unnecessarily heavy and inappropiate, as will be shown hereafter.
The present invention relates to a new and characteristic design of a wrist pin which is light yet highly resistant, applicable to connect the parts of an articulated or two-piece piston and for coupling the piston to a connecting rod in an internal combustion engine.